PURPOSE: To prevent the idling of a turbine rotor by preventing gland steam from flowing into a low pressure turbine during the stoppage of a steam turbine.

CONSTITUTION: A bypass line 21 which branchs off from the halfway of a bleed pipe 12 extending from a middle pressure turbine 2 to a low pressure feed water heater 11 and extends to a condenser 5 is provided, and moreover provided with a cutoff valve 22. In addition, a leaking steam pipe 13 extending from the inner gland of a high pressure turbine 1 to the halfway of the bleed pipe 12 is provided with a cutoff valve 23. During the stoppage of a steam turbine, the cutoff valve 22 is opened to directly flow gland steam through the bypass line 21 to the condenser 5, and the cutoff valve 23 is closed to shut off leaking gland steam for preventing the gland steam from flowing into a low pressure turbine 3. At the same time, the vacuum adjusting valve 14 of the condenser can be opened to lower the vacuum pressure in the condenser, and a jacking oil pump can be stopped once to reduce the number of revolutions of the turbine.